Railway signaling system



1929- L. o. GRONDAHL ET AL 1,730,135

RAILWAY SIGNALING SYSTEM Filed Dec. 18, 1928 INVENTORS UM- Anonm @ct. l,l929 UNHTEE earner; tries LABS 0. GBONDAHL, PITTSBURGH, AND EAUL N.BOSSART, OF SVTISSVALE, PENN- SYLVANIA, ASSIGIIORS TO THE UNION SVTITCH8r, SIGNAL COMEANY, OF SWISS VALE, PENNSYLVANIA, A CORPORATION OFPENNSYLVANIA BAILVJAY SIGNALING SYSTEM Application filed December 18,1928. Serial No. 326,724.

Our invention relates to railway signaling systems, and particularly tosystems of the type involving direct current apparatus operated from asource of alternating current through the medium of rectifiers.

One object of our invention is the provision of a novel and improvedsystem of this character having certain features which render itpeculiarly safe and efficient.

We will describe one form of system embodying our invention, and willthen point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form ofsignaling system embodying our invention.

Referring to the drawing, the reference characters 1 and 1 designate thetrack rails of a railway along which traflic normally moves in thedirection indicated by the arrow. These rails are divided by insulatedjoints 2 into a plurality of successive track sections, of which onlytwo complete sections AB and BG, are shown in. the drawing.

Each section is provided with means, hereinafter explained, forsupplying the track rails with pulsating signaling current of normal orreverse polarity depending on traffic conditions in advance of thesection.

Located at the entrance end of each section are two transformers T and Tthe primary 3 of each of which is connected across the rails of thesection. Interposed between one rail and the primary 8 of eachtransformer T is a rectifier 6 which permits current of reversepolarity, but not of normal polarity, to pass through the transformerprimary. A similar rectifier 6 is associated with each transformer T topermit current of normal polarity, but not of reverse, to pass throughthe primary of this transformer. The secondary 4 of each transformer Tis connected with the input terminals of a full-wave rectifier F or Fand the secondary circuit of each transformer includes a condenser 7 fortuning the circuit to the frequency of the sig naling current in thetrack rails. The trans.- formers should have relatively large leakageresistance so that their secondary circuits may be sharply tuned. Theoutput terminals of each rectifier F are connected with the windmg 8 ofa three position relay D, and the output terminals of each rectifier Fare connected with the other winding 8 of the same relay. The windings 8and 8 of each relay D control an armature 9 in such manner that thisarmature is swung to the left when winding S is energized, but is swungto the right when winding 8 is energized, and 00-- cupies anintermediate posit-ion when both the windings are de-energized. Thearmature 9 of each relay D operates contact fingers 10 and 11 forpurposes hereinafter explained.

Reverting now to the supply of current to the track rails, each sectionis provided with a line transformer designated by the referencecharacter L with an exponent corresponding to the location. The primary15 of each of these transformers is connected with a transmission lineN,which is constantly supplied with alternating current from a generatorK. Secondary 14 of each transformer L is connected with the track railsof the corresponding section, and a polarizing rectifier 12 or 12 isinterposed in this con nection in the followng manner: Considering, forexample, section AB, when relay D for the section next in advance isdeenergized, rectifier 12 is interposed between transformer secondary 14and track rail 1. This rectifier permits the negative half of eachalternating current wave to flow through the track rails, but preventsthe positive half of each wave from reaching'the rails. When relay D isenergized in either the normal or the reverse direction, however,rectifier 12 is interposed between the secondary 14 and track rail 1 insuch manner as to permit the positive half of each wave to flow but toprevent the negative half of each 'wave from reaching the track rails.It follows that the rails of each section are supplied with pulsatingcurrent of reverse or normal polarity according as the section next inadvance is I occupied or unoccupied.

G, Y and R, arranged when lighted to indicate respectively proceed,caution and stop. These lamps are controlled by contact 11 of theassociated relay D in such manner that lamp G is lighted when the relayis energized in the normal direction, lamp Y is lighted when the relayis energized in the reverse direction, and lamp R is lighted when therelay is deenergized.

As shown in the drawing, the section'to the left of point A is occupiedbya car or train represented by an axle and a pair of wheels W, so thatboth windings S and 8 of relay D are de-energized, with tne result thatthe armature and contacts of this relay occupy their intermediatepositions. Lamp R of signal S is therefore lighted, so that this signalindicates stop. Contact 10 of relay D being in the intermediateposition, polarizing rectifier 12 is connected in the track circuit forsection AB, so that only negative half waves are supplied to this trackcircuit, with the result that winding S of relay D is energized, andwinding 8 of this relay is de-energized. Relay D is accordinglyenergized in the reverse direction, so that its armature and contactsare swung to the left. Lamp Y of signal S therefore lighted, so thatthis signal indicates caution. Contact 10 of relay D being in itsleft-hand position, the normal polarizing rectifier 12 is interposed inthe track circuit for section B-C, so that winding 8 of relay D isenergized, and winding 8 of this relay is de-energlzed. The armature andcontacts of relay D are accordingly swung to the right, so that lamp Gof signal S 1s lighted and the signal lndicates proceed. Polarizingrectifier 12 is included in the track circuit for the section to theright of point C, so that the signal for such section will indicateproceed.

The transformers and condensers associated with each relay D serve toabsolutely prevent false operation of these relays by direct foreigncurrent. Furthermore, the current which is used for the track circuitsis coded in that every other half wave is eliminated, with the resultthat the system provides absolute protection against false operation ofthe track relays by alternating foreign cur rent even when this currentis of the same frequency as that of the signaling current; the reasonfor this is, that alternating current would energize both windings ofeach relay equally, and so would have no effect on the armature. Anotherfeature of our in vention is that the power required by the system isconsiderably less than that which is required for the operation ofalternating current relays.

Although we have herein shown and described only one form of railwaysignaling system embodying our invention, it is understood that variouschanges and modifications may be made therein within the scope of theappended claims without departing from the spirit and scope of ourinvention.

Having thus described our invention, what we claim is:

1. In combination, a section of railway track, means for supplying therails of said section with pulsating current of normal or reversepolarity, two transformers the primaries of which are connected with therails of said section, rectifiers associated with said primaries forpermitting current of normal polarity but not of reverse to pass throughone primary and for permitting current of reverse polarity but not ofnormal to pass through the other primary, two full wave rectifiersconnected with the two secondaries respectively of said transformers,two relay windings supplied with current from said two full waverectifiers respectively, and signaling means for said section controlledby said relay windings.

2. In combination, a section of railway track, means for supplying therails of said s ction with pulsating current of normal or reversepolarity, two transformers the primaries of which are connected with therails of said section, rectifiers associated with said prin'iaries forpermitting current of normal polarity but not of reverse to pass throughone primary and for permitting current of reverse polarity but not ofnormal to pass throughthe other primary, two full wave rectifiersconnected with the two secondaries respectively of said transformers, acondenser in the secondary circuit of each transformer for tuning suchcircuit at the frequency of the pulsating current in the track rails,two relay windings supplied with current from said two full waverectifiers respectively, and signaling means for said section controlledby said relay windings.

3. In combination, a section of railway track, means for supplying therails. of said section with pulsating current of normal or reversepolarity, two transformers the primaries of which are connected with therails of said section, rectifiers associated with said primaries forpermitting current of normal polarity but not of reverse to pass throughone primary and for permitting current of reverse polarity but not ofnormal to pass through the other primary, two full wave rectifiersconnected with the two secondaries respectively of said transformers, athree position relay having two windings supplied with current from saidtwo full wave rectifiers respectively whereby said relay is energized innormal or reverse direction according as the current in the track railsis of nor mal or reverse polarity, and signaling means for said sectioncontrolled by said relay.

4. A railway signaling system comprising a stretch of track divided intosections, two transformers for each section the primaries of which areconnected with the rails of the section, rectifiers for each section forpermitting current of normal polarity but not of reverse to pass throughthe primary'of one associated transformer and for permitting current ofreverse polarity but not of normal to pass through the primary of theother associated transformer, a full wave rectifier connected with thesecondary of each transformer, a three position relay for each sectionhaving two windings separately supplied with current from the two fullwave rectifiers associated with the section whereby said relay isenergized in normal or reverse direction according as the current in therails of the section is of normal or reverse polarity, means controlledby the relay for each section for supplying the rails of the sectionnext in the rear with pulsating current of normal polarity when therelay is energized in either the normal or reverse direction and withpulsating current of reverse polarity when the relay is de-energized,and signaling means for said sections controlled by said relays.

5. A railway signaling system comprising a stretch of track divided intosections, two transformers for each section the primaries of which areconnected with the rails of the section, rctifiers for each section forpermitting current of normal polarity but not of reverse to pass.through the primary of one associated transformer and for permittingcurrent of reverse polarity but not of normal to pass through theprimary of the other associated transformer, a full wave rectifierconnected with the secondary of each transformer, a three position relayfor each section having two windings separately supplied with currentfrom the two full wave rectifiers associated with the section wherebysaid relay is energized in normal or reverse direction according as thecurrent in the rails of the section is of normal or reverse polarity,means controlled by the relay for each section for supplying the railsof the section next in the rear with pulsating current of normalpolarity when the relay is energized in either the normal or reversedirection and with pulsating current of reverse polarity when the relayis de-energized, a condenser in the secondary circuit of each saidtransformer for tuning such circuit at the frequency of the pulsatingcurrent in the track rails, and signaling means for said sectionscontrolled by said relays.

6. A railway signaling system comprising a stretch of track divided intosections, two transformers for each section the primaries of which areconnected with the rails of the section, rectifiers for each section forpermitting current of normal polarity but not of reverse to pass throughthe primary of one associated transformer and for permitting current ofreverse polarity but not of normal to pass through the primary of theother associated transformer, a full wave rectifier connected with thesecondary of each transformer, a three position relay for each sectionhaving two windings separately supplied with current from the two fullwave rectifiers associated with the section whereby said relay isenergized in normal or reverse direction according as the current in therails of the section is of normal or reverse polarity, a source ofalternating current connected with the rails of each section, twopolarizing rectifiers for each section, means operating when each relayis energized in either the normal or the reverse direction to interposeone of said polarizing rectifiers between said source and a track railof the section next in the rear and thereby permit current of normalpolarity but not of reverse to flow, means operating when each relay isde-energized to interpose the other polarizing rectifiers between saidsource and a track rail of the section next in the rear and therebypermit current of reverse polarity but not of normal to flow, andsignaling means for said sections controlled by said rectifiers.

In testimony whereof we aflix our signatures.

LAR-S O. GRONDAHL. PAUL N. BOSSART.

